This application is based on and claims the benefit of German Patent Application No. 199 00 944.9 filed Jan. 13, 1999, which is incorporated by reference herein.
The invention concerns an optical cable for routing in sewers having a cable core and a metallic cladding encircling the cable core, in which the cable core comprises several stranding elements each having a sheath encircling several optical waveguides.
From the Alcatel leaflet xe2x80x9cFastxe2x80x94the Optical Fiber Cable System for Cable Systems in Urban Sewers.xe2x80x9d an optical cable is known that consists of a central member around which six bundle conductors are stranded. A corrugated metallic outer cladding encircles the cable ropes. A plastic cladding can be arranged on the outer cladding. Every bundle conductor has 24 fibers resulting in a total of 144 fibers. The outside diameter of this known cable is 15 mm. The optical waveguides are present in the bundle units with an excess length.
The known cable covers all applications in sewers. Only materials which are resistant for the special requirements in sewers are used. Special cladding composites offer protection against aggressive chemicals. The metal cladding represents a second protective shield and provides the greatest degree of protection against rodents. The plastic outer cladding and the metal cladding hermetically protect the sensitive core of the optical waveguide cable like armor against the aggressive environment.
The large outside diameter, however, with respect to the number of the fibers accommodated is a drawback of this cable. A further drawback is the insufficient modularity, i.e., access to the individual fibers can be improved.
The present invention is therefore based on the object of improving the known optical cable such that with the same outside cable diameter, a higher number of fibers are contained in the cable and that the distribution of the fibers in the cable is optimized, i.e., a large number of wires is accommodated in the cable.
This object is achieved by an optical cable for routing in sewers having a cable core and a metallic cladding encircling the cable core, in which the cable core comprises several stranding elements each having a sheath encircling several optical waveguides, wherein: each stranding element comprises a bundle of a plural optical waveguides running substantially parallel to each other and being unstranded or stranded with large pitch; each bundle is encircled by a sheath tightly encircling the bundle; and plural said stranding elements are stranded to form the cable core, with the cable core being composed exclusively of such bundles.
Additional advantageous features of the invention will be apparent from the description below and the appended claims.
While in the known cable, the outside diameter of the cable core with a fiber count of 144 is around 7.8 mm, the outside diameter of the cable core of the cable according to the invention of the same fiber count is less than 6.0 mm.